For your issue 1: Every time you create a signature, the catalog gets updated, which means it needs to be delivered to the endpoints again. So, this is working as designed.
For your issue 2: The agents will report back to BigFix that the catalog was installed, but BFI won’t know about it until the next scheduled or manual import occurs. So, over time, those endpoints will drop from the catalog not updated chart.
After the catalog is updated these new signatures will be used the next time the scanner is executed by the agent. Keep in mind, it could be up to 7 more days before this happens, assuming the standard scan schedule.
Hope this helps.